The invention relates to a method for representing the surface of an object.
A method is known from EP 553 266 B1 for determining the 3D coordinates of the surface of an object in which the surface of the object is sampled by a scanner. The 3D coordinates are determined by an evaluation system in the scanner reference system. A tracking system is furthermore present which can determine the position and direction of the scanner. The absolute 3D coordinates of the surface of the object can be determined by the evaluation system from the 3D coordinates in the scanner reference system and from the data of the position and direction of the scanner in the absolute reference system. These data can be recorded and/or displayed.
EP 995 108 B1 discloses a method for the automatic recognition of surface defects on body shells of automotive vehicles in which a projection apparatus projects a grid structure onto the body shell. The light reflected from the surface of the body shell is received by an optical measurement apparatus and is supplied to a computer system as a measured signal. Surface defects can be recognized in the computer system which can be marked by a marking apparatus.
Methods for representing the surface of an object are used in component inspection, in particular in the automotive industry, but also in other branches of industry. In this respect, the actual 3D data of the surface of the object can be determined by a 3D measurement system. These actual 3D data, which can be present in the form of a scatter plot, for example, can be displayed, in particular on the screen of a computer or of a PC. The surface of the object represented in this manner can be observed and evaluated by a person.
The esthetic, defect-free finish of the visible surface of a product is a decisive quality feature. It allows conclusions on the quality and rating of the product. A high significance is therefore attached to a high-quality surface by quality management, in particular in the automotive industry, but also in other industries.
A number of surface defects, however, only become visible when the surface is shiny and when the environment is reflected in it. The shininess of a surface is usually produced by a surface coating, for example by varnishing, anodization, chromium plating or similar processes. This process step is, however, at the very end of the value creation chain so that the elimination of defects which are only recognized here is frequently no longer possible at all or can only be achieved with a large effort, which is associated with correspondingly high costs.
It is therefore desirable for reasons of economy to be able to recognize surface defects at the earliest possible point in the value creation chain. Surface defects can, however, only be recognized and evaluated with difficulty on matt surfaces.
For example with a body part of an automotive vehicle, a component with a matt surface is produced in a first process stage which takes place in the pressing plant. In a second process stage, a shell is produced whose surface is likewise still matt. The component is only painted in a third process step, which results in a shiny surface. Surface defects can only now be adequately recognized and evaluated.
It had previously been attempted with the help of a complex quality management already to evaluate in advance in the early process stages the surface defects visible later in the finished product. Various aids are used for this purpose, for example whetstones, shine-producing oils, special light sources and similar. On the one hand, all these processes are time-intensive and they require a very large amount of experience by the user. On the other hand, these processes also still leave a large leeway with respect to the very subjective evaluation of the defects.
A further possibility is to convey sample parts through the complete process chain up to painting in order to be able actually to evaluate the appearance on the finished product. This process, however, takes a long time and is very expensive.